1. Field of the Invention
The present invention relates to a fixing member such as a heat roll, belt and the like used in a fixing portion and the like of a copying apparatus, printer, and other various image forming apparatuses used in an electrophotography method in which the member is always exposed to heating and cooling cycles and mechanical press-contacting, a primer composition suitably used for such a fixing member, and a fixing device using such a fixing member.
2. Description of the Related Art
As a method for fixing a toner image formed on paper in a copying apparatus, a printer, and other various image forming apparatuses used in an electrophotography method, there is usually adopted a method in which a supporting substrate such as paper and the like on which a toner image is formed is passed between two rotating members which are heated by a heat generating body such as a lamp and the like placed thereabout and press-contacted with each other, to fuse the toner image on the supporting substrate.
As one example of the fixing device used in such a method, a heat roll fixing device as shown in FIG. 1 is listed, and this heat roll fixing device is composed of a pair of rolls being a heat roll 1 and a pressure roll 11. The heat roll 1 comprises hollow core metal 2 in the form of a cylinder composed of aluminum, iron, and the like having a surface coated with a fluororesin layer 4 composed of a heat resistant elastomer or heat resistant resin having excellent releasing properties such as a fluorine-based resin such as fluororubber, silicone rubber, polytetrafluoroethylene (PTFE), a copolymer of tetrafluoroethylene with perfluoroalkylvinyl ether (PFA), and the like. Further, inside the heat roll 1, a heat generating body 21 such as a halogen lamp and the like is placed to impart a heat roll function to the roll 1.
On the other hand, the pressure roll 11 comprises hollow core metal 12 in the form of a cylinder composed of aluminum, iron, and the like having a surface coated with a fluororesin layer 14 composed of a heat resistant elastomer or heat resistant resin having excellent releasing properties of the same kind or of a different kind from those used for the heat roll 1. The heat roll 1 and the pressure roll 11 are press-contacted with each other by a spring and the like. In FIG. 1, 27 indicates an inlet, 28 indicates an outlet, and 29 indicates a releasing agent application apparatus which applies a releasing agent to the surface of the heat roll 1.
In this heat roll fixing device, paper 31 carrying a toner image 32 on the surface is conveyed between the heat roll 1 and the pressure roll 11, and the toner image 32 is fixed on the paper 31, then, the paper 31 is conveyed by a pair of rolls through the outlet 28.
The fixing member coated on the surface of a substrate such as a roll and the like is required not to cause a hot offset phenomenon in which a part of a fused toner image adheres to the rotating member, and the phenomenon in which a toner image does not separate from the rotating member and is curled onto the rotating member together with the substrate.
On the other hand, since a heating and cooling cycle is repeated in which the fixing member is heated to temperatures as high as 200.degree. C. as the setting temperature when the apparatus is operating and cooled down to room temperature when the operation is terminated, the fixing member is also required to be able to tolerate this cycle. Further, on the outermost surface of the rotating member, the fixing members installed facing each other are press-contacted against each other, and the fixing member is placed under severe stress from a stripping finger for preventing paper curl which is always press-contacted with the member, and the like.
Therefore, the heat resistant elastomer or heat resistant resin having excellent releasing properties coated on a rotating member of a fixing apparatus is limited to silicone-based or fluorine-based polymer materials such as fluororubber, silicone rubber, fluororesin, and the like. Unfortunately, although these polymer materials have excellent releasing properties, their adhesion to a substrate such as metal and the like is poor, therefore, it is difficult to coat them directly as a surface layer in producing a heat roller.
Hence, as a method for coating a fluororesin having low adhesion on the surface of a substrate, there is suggested a method in which an adhesive member called primer is inserted between the fluororesin layer and the metal surface.
For example, regarding a case in which a PFA resin is used as a fluororesin, Japanese Patent Application Laid-Open (JP-A) No. 57-177067 suggests a method in which hollow core metal and a PFA resin layer are adhered via an adhesive primer containing a PFA resin and a polyimide precursor obtained by reaction of pyromellitic anhydride with diaminodiphenyl ether, diaminodiphenylmethane, and the like. Japanese Patent Application Laid-Open (JP-A) No. 63-112674 suggests a method in which hollow core metal and a PFA resin are adhered by an adhesive primer containing in a mixed solvent of a water-soluble organic solvent with water, a PFA resin and a material obtained by neutralizing with amine an aromatic polyimide precursor or free carboxylic acid thereof prepared by reacting pyromellitic anhydride with 4,4'-diaminodiphenylsulfone, as main components.
Further, regarding a case in which a PTFE resin is used instead of a PFA resin as a fluororesin, U.S. Pat. No. 4,049,863 describes a primer containing PTFE, colloidal silica, and polyamideimide (PAI) in which the ratio of PTFE to PAI is 1:9, and suggests coating this primer on a metal core roll which has been surface-treated by grid blasting, flame fusing or frit coating with metal or metal oxide, or phosphoric acid, chromic acid or the like, so as to obtain a dry film thickness of 2 to 15 .mu.m. U.S. Pat. No. 3,801,379 suggests coating poly(arylene sulfide) containing 5 to 20% PTFE on an aluminum substrate after treatment of the surface of a core roll with hot water or vapor. Canadian Patent No. 887,122 suggests conducting coating in gradated structure conditionusing PAI and PTFE. Further, U.K. Patent No. 1,512,495 suggests that in PAI coating containing a PTFE powder, the minimum ratio of PTFE to PAI is 1:7.
Particularly, in fixing members used in an image forming apparatus in electrophotography mode, as an example of a fixing member obtained by adhering a fluororesin layer to a substrate such as metal and the like by a primer, Japanese Patent Application Laid-Open (JP-A) No. 64-1534 suggests a fluororesin-coated cylindrical member obtained by heat-fusing a heat-flowable fluororesin tube containing a filler onto a cylindrical member whose surface has been treated previously with a primer containing a fluororesin. Japanese Patent Application Laid-Open (JP-A) Nos. 4-8543, 4-45931 and 4-78533 suggest a fluororesin-coated cylindrical member obtained by heat-fusing a fluororesin tube onto a cylindrical member having a primer layer containing a polyparabanic acid resin or polyimide resin.
These primers contain as the main component a heat resistant resin such as a polyamide, polyimide, polyamideimide, polyarylene sulfide, and the like and have the drawbacks that when a substrate and a fluororesin are adhered using the above-described adhesive primer or in the case of a fixing member obtained by adhering a fluororesin layer to a substrate such as metal and the like by a primer, adhesion between the fluororesin layer and the substrate such as metal and the like exhibits excellent results in the initial stages, however, under the severe conditions of use for a fixing member used in an electrophotographic type image forming apparatus, deterioration with age occurs and the fluororesin peels easily off the substrate, and therefore the life span thereof is not long.